JP4032803B2 - Gallium nitride compound semiconductor device and manufacturing method thereof - Google Patents

Abstract

In a gallium nitride semiconductor device comprising an active layer made of an n-type gallium nitride semiconductor that includes In and is doped with n-type impurity and a p-type cladding layer made of a p-type gallium nitride semiconductor that includes Al and is doped with p-type impurity, a first cap layer, made of a gallium nitride semiconductor that includes n-type impurity of lower concentration than that of said active layer and p-type impurity of lower concentration than that of said p-type cladding layer, and a second cap layer made of a p-type gallium nitride semiconductor that includes Al and is doped with p-type impurity are stacked one on another between said active layer and said p-type cladding layer. <IMAGE>

Description

[0001]
[Industrial application fields]
The present invention relates to a nitride semiconductor (In_XAl_YGa_1-XYThe present invention relates to a gallium nitride compound semiconductor device using N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and more particularly to a gallium nitride compound semiconductor device having an active layer containing In.
[0002]
[Prior art]
Gallium nitride compound semiconductor elements using nitride semiconductors are light emitting elements such as light emitting diode elements (LEDs) and laser diode elements (LD), light receiving elements such as solar cells and photosensors, or electrons such as transistors and power devices. Used for devices. In particular, a semiconductor laser element using a nitride semiconductor is considered to be capable of oscillating in a wide range of visible light from the ultraviolet region to the red region. It is expected to be a wide variety of light sources such as networks.
[0003]
Conventional gallium nitride-based compound semiconductor elements often have a hetero pn junction in which an n-type active layer containing In and a p-type cladding layer containing Al are combined in a basic configuration. In addition, since the n-type active layer containing In is easily decomposed, in order to prevent decomposition of the active layer when growing the p-type cladding layer at a relatively high temperature, the n-type active layer is interposed between the n-type active layer and the p-type cladding layer. In many cases, a cap layer made of AlGaN is formed into a thin film.
[0004]
As an example of a conventional gallium nitride-based compound semiconductor device, a schematic cross-sectional view of a nitride semiconductor laser is shown in FIG. The nitride semiconductor laser of FIG. 3 has a double heterostructure in which an MQW active layer made of InGaN is sandwiched between n-type and p-type AlGaN cladding layers. An n-type AlGaN contact layer 103, an n-type InGaN crack prevention layer 104, an n-type AlGaN / GaN superlattice clad layer 105, an undoped GaN light guide layer 106, on a GaN substrate 101 on which ELOG is grown, via a buffer layer 102, A quantum well active layer 107 made of InGaN, a p-type AlGaN cap layer 108, an undoped GaN light guide layer 109, a p-type AlGaN / GaN superlattice cladding layer 110, and a p-type GaN contact layer 111 are stacked in this order. 162 is ZrO.₂Protective film made of 164 is SiO₂And TiO₂A dielectric multilayer film, 120 is a p-electrode, 121 is an n-electrode, and 122 and 123 are extraction electrodes.
[0005]
The active layer 107 is made of undoped In_x1Ga_{1- x1}N well layer (0 <x1 <1) and Si-doped In_x2Ga_{1- x2}It has an MQW structure in which N barrier layers (0 ≦ x2 <1, x1> x2) are alternately and repeatedly stacked an appropriate number of times. The p-type AlGaN cap layer 108 forms a hetero pn junction with the active layer 107, effectively confining electrons in the active layer 107 and lowering the laser threshold. The p-type cap layer 108 plays a role of supplying holes to the active layer 107 and is therefore doped with high-concentration Mg. The p-type cap layer 108 may be grown as a thin film having a thickness of about 15 to 500 mm, and if it is a thin film, it can be grown at a lower temperature than the p-type light guide layer 109 and the p-type optical cladding layer 110. Therefore, by forming the p-type cap layer 108, decomposition of the active layer 107 containing In can be suppressed as compared with the case where the p-type light guide layer 109 and the like are formed directly on the active layer.
[0006]
With the gallium nitride compound semiconductor laser having the structure shown in FIG. 3, it is possible to achieve a lifetime exceeding 10,000 hours under the condition of continuous oscillation at room temperature and 5 mW.
[0007]
[Problems to be solved by the invention]
However, gallium nitride-based compound semiconductor devices are required to have a further improved device life in order to expand their applications. In particular, for a gallium nitride-based compound semiconductor laser, improvement in device lifetime is extremely important, and further, improvement in threshold characteristics during high-temperature operation is also required.
[0008]
[Means for Solving the Problems]
The present inventor has found that in the gallium nitride-based compound semiconductor device, (1) the lower the impurity concentration of the p-type cap layer adjacent to the n-type active layer, the better the device life and temperature characteristics, and (2) As a result of the n-type and p-type impurities canceling each other out at the pn junction interface between the n-type active layer and the p-type cap layer, the present invention has been made by paying attention to the presence of impurities that do not contribute to carrier generation. .
[0009]
The point (2) will be described in detail with reference to FIG. FIG. 2A is a schematic diagram showing a state of a pn junction interface between a p-type cap layer and an n-type active layer in a conventional nitride semiconductor device. As shown in the figure, the p-type impurity 10 doped in the p-type cap layer emits holes, and the n-type impurity 12 doped in the n-type active layer emits electrons. It becomes a carrier and forms an element current. However, when the p-type cap layer is grown on the n-type active layer, the p-type impurity 10 in the p-type cap layer partially penetrates into the n-type active layer by thermal diffusion. The n-type impurity 12 partially penetrates into the p-type cap layer by thermal diffusion. For this reason, a part of the p-type impurity 10 and a part of the n-type impurity 12 are mixed in the same region near the pn junction interface, and the donor and the acceptor compensate and do not contribute to effective carrier generation.
[0010]
  Therefore, a gallium nitride compound semiconductor device according to the present invention includes an active layer made of an n-type gallium nitride compound semiconductor doped with n-type impurities and a p-type gallium nitride-based compound containing Al and doped with p-type impurities. A gallium nitride-based compound semiconductor element having a p-type cladding layer made of a compound semiconductor, comprising a first cap layer made of a gallium nitride-based compound semiconductor between the active layer and the p-type cladding layer, and Al laminating a second cap layer made of a p-type gallium nitride compound semiconductor doped with a p-type impurity;The first cap layer includes an n-type impurity having a lower concentration than the active layer and a p-type impurity having a lower concentration than the second cap layer,The n-type impurity concentration of the first cap layer is high on the side close to the active layer,To be lower on the side closer to the second cap layerThe p-type impurity concentration of the first cap layer is higher on the side closer to the second cap layer, and decreases with increasing distance from the active layer;To be lower on the side closer to the active layerIt is characterized by decreasing with increasing distance from the second cap layer.
[0011]
Preferably, the first cap layer is formed in contact with the active layer, and the second cap layer is formed in contact with the first cap layer. More preferably, a p-type light guide layer is formed in contact with the second cap layer.
[0012]
FIG. 2B is a schematic diagram showing the state of the pn junction interface between the p-type cap layer and the n-type active layer in the nitride semiconductor device according to the present invention. As shown in FIG. 2B, according to the present invention, the n-type active layer and the p-type cap layer (= Since the second cap layer is provided between the second cap layer and the p-type cap layer containing a high-concentration impurity directly contacts the n-type active layer (in the case of FIG. 2A), the donor and acceptor are compensated. Can be suppressed. Therefore, the doping amount of the p-type impurity into the p-type cap layer (= second cap layer) can be reduced by the amount of compensation, and the device life and characteristic temperature can be improved.
[0013]
The impurity concentration in the final device is not particularly limited, but the concentration of the n-type impurity and the p-type impurity in the first cap layer is 1.0 × 10 6.¹⁷cm^-3The concentration of the p-type impurity in the second cap layer is 8.0 × 10¹⁸~ 2.0 × 10¹⁹cm^-3It is preferable that In the present invention, the concentration of the n-type impurity and the p-type impurity in the first cap layer is an average value in the thickness direction of the layer. The concentration of the n-type impurity and the p-type impurity in the first cap layer has a concentration gradient in the layer thickness direction due to the influence of thermal diffusion from other layers. That is, the n-type impurity concentration in the first cap layer is high on the side close to the active layer and decreases as the distance from the active layer increases. Conversely, the p-type impurity concentration in the first cap layer is It is higher on the side closer to the cap layer, and decreases as the distance from the second cap layer increases.
[0014]
In order to effectively suppress donor and acceptor compensation, the first cap layer is preferably grown without doping with n-type impurities and p-type impurities. Even when grown without doping impurities, the first cap layer contains n-type impurities by thermal diffusion from the active layer and p-type impurities by thermal diffusion from the second cap layer. become.
[0015]
Since the first cap layer having a low impurity concentration is a high resistance layer, the first cap layer is preferably thin from the viewpoint of suppressing the driving voltage of the element. On the other hand, from the viewpoint of suppressing cancellation of p-type impurities and n-type impurities, it is preferable that the first cap layer is thicker. The effect of suppressing the compensation of the acceptor and the donor is that the n-type impurity doped in the active layer has a thermal diffusion length indicated in the first cap layer and the p-type impurity doped in the second cap layer is the first cap layer. It becomes maximum when the total length with the thermal diffusion length shown in the figure is approximately equal to the film thickness of the first cap layer. At this time, there is theoretically no region where the p-type impurity thermally diffused from the second cap layer and the n-type impurity thermally diffused from the n-type active layer coexist. Here, the thermal diffusion length exhibited by the n-type and p-type impurities in the first cap layer is based on the value indicated in the process in which the thermal diffusion of the impurities into the first cap layer occurs most actively. That is, “the thermal diffusion length exhibited by the n-type impurity in the first cap layer” refers to the thermal diffusion length exhibited by the n-type impurity at the growth temperature (absolute temperature) of the first cap layer. “The thermal diffusion length exhibited by the p-type impurity in the first cap layer” refers to the thermal diffusion length exhibited by the p-type impurity at the growth temperature (absolute temperature) of the second cap layer. When the active layer having a multi-quantum well structure having at least a well layer and a barrier layer ends in an undoped state, the total film thickness of the undoped layer and the first cap layer is equal to the above thermal layer. When the diffusion length is equal to the total, the impurity compensation suppressing effect is maximized. For example, when an active layer having a multiple quantum well structure in which non-doped well layers and n-type impurity-doped barrier layers are alternately stacked ends with the non-doped well layer, the total thickness of the well layer and the first cap layer Is equal to the sum of the thermal diffusion lengths, the impurity compensation suppression effect is maximized.
Here, the thermal diffusion length L refers to the diffusion length of impurities after t seconds, and L is determined by the square root of (D · t) (L is a theoretical value). Here, D is a diffusion constant, and D = D₀・ A²exp (−U / kT), D₀Is the initial diffusion constant, a is the lattice constant of the material, U is the potential energy of the material, k is the Boltzmann constant, and T is the temperature.
[0016]
The first cap layer includes, for example, a GaN layer, In_xGa_{1- x}N layer (0 <x <1) and Al_yGa_{1- y}An N layer (0 <y <1) can be used, and a laminate of two or more of these can be used. The GaN layer is preferable in that it is effective in suppressing In dissociation in the active layer and can easily form a layer having good crystallinity. In_xGa_{1- x}Even if the N layer is formed as a thick film, the V layer_fIs preferable in that it can be stacked with good crystallinity. The AlyGa1-yN layer (0 <y <1) is preferable in that it is most effective in suppressing the dissociation of In in the active layer.
[0017]
As described above, the preferable film thickness of the first cap layer varies depending on the composition of the first cap layer because n-type and p-type impurities depend on the thermal diffusion length exhibited in the first cap layer. For example, when the first cap layer is composed of a GaN layer, the thickness of the first cap layer is desirably 15 to 100 mm (more preferably 50 to 80 mm). The first cap layer is In_xGa_{1- x}In the case of N layers (0 <x <1), a film thickness of 15 to 150 mm (more preferably 85 to 115 mm) is desirable. The first cap layer is Al_yGa_{1- y}In the case of N layers (0 <y <1), a film thickness of 15 to 50 mm (more preferably 20 to 50 mm) is desirable.
[0018]
On the other hand, the thickness of the second cap layer is preferably 15 to 500 mm in order to obtain a film having good crystallinity at a low temperature.
[0019]
The active layer may be a gallium nitride compound semiconductor containing In and doped with an n-type impurity, and may be any of a bulk, a single quantum well structure, and a multiple quantum well structure. Among them, it is preferable to have an active layer having a quantum well structure in which a well layer made of a gallium nitride compound semiconductor containing In and a barrier layer made of a gallium nitride compound semiconductor to which an n-type impurity is added are alternately stacked. In that case, the first cap layer contains an n-type impurity at a concentration lower than that of the barrier layer.
[0020]
Examples of the n-type impurity used in the gallium nitride compound semiconductor device of the present invention include Si, Ge, Sn, S, O, and the like, and preferably Si and Sn. The p-type impurity is not particularly limited, and examples thereof include Be, Zn, Mn, Cr, Mg, and Ca, and Mg is preferably used.
[0021]
In this specification, undoped refers to growing without adding p-type impurities, n-type impurities or the like as dopants during growth of a nitride semiconductor. For example, in an organic metal vapor phase growth method, In this case, the growth is performed without supplying the dopant as an impurity.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The gallium nitride compound semiconductor element of the present invention includes GaN, AlN, InN, or a mixed crystal gallium nitride compound semiconductor (In_XAl_YGa_1-XYN, 0.ltoreq.X, 0.ltoreq.Y, X + Y.ltoreq.1) can be used, and a mixed crystal in which a part thereof is substituted with B or P may be used.
Here, a gallium nitride compound semiconductor laser will be described as an example of a gallium nitride compound semiconductor device.
[0023]
FIG. 1 is a sectional view showing a gallium nitride compound semiconductor laser according to the present invention. The nitride semiconductor laser shown in FIG._aGa_{1- a}An active layer 107 made of N (0 ≦ a <1) is formed of n-type Al._bGa_1-bN (0 ≦ b <1) layers 103 to 106 (b values differ for each layer) and p-type Al_cGa_1-cIt is sandwiched between N (0 ≦ c <1) layers 108 to 111 (the value of c is different for each layer), and a so-called double heterostructure is formed.
[0024]
The active layer 107 is made of In_x1Ga_{1- x1}N well layer (0 <x1 <1) and In_x2Ga_{1- x2}It has an MQW structure (multiple quantum well structure) in which N barrier layers (0 ≦ x2 <1, x1> x2) are alternately and repeatedly stacked an appropriate number of times. The well layer is undoped, while all the barrier layers are doped with n-type impurities such as Si and Sn. By doping the barrier layer with the n-type impurity, the initial electron concentration in the active layer is increased, the electron injection efficiency into the well layer is increased, and the light emission efficiency of the laser is improved. The active layer 107 may end with a well layer or a barrier layer. Since a relatively large amount of InN having a high vapor pressure is mixed in the active layer 107, it is easily decomposed and is grown at a lower temperature (about 900 ° C.) than the other layers.
[0025]
The cap layer 108 is composed of two layers, a first cap layer 108a grown undoped and a second cap layer 108b grown by doping high-concentration Mg.
[0026]
The first cap layer 108a serves to prevent compensation between Si doped in the barrier layer of the n-type active layer 107 and Mg doped in the second cap layer 108b. For example, the GaN layer, In_xGa_{1- x}N layer (0 <x <1), Al_yGa_{1- y}The N layer (0 <y <1) or a laminate of two or more of these is grown undoped. The film thickness of the first cap layer 108a is about 15 mm or more. The thermal diffusion length indicated by Si doped in the active layer 107 in the first cap layer 108a and Mg doped in the second cap layer 108b. It is below the total length with the thermal diffusion length shown in the 1st cap layer 108a. Here, the thermal diffusion length L indicated by Si and Mg in the first cap layer 108a can be expressed by the above formula. This prevents mixing of Si thermally diffused from the n-type active layer 107 and Mg thermally diffused from the second cap layer 108b grown next.
[0027]
The first cap layer 108a is made of a GaN layer, In_xGa_{1- x}N layer (0 <x <1), Al_yGa_{1- y}Of the N layers (0 <y <1), two or more kinds of stacked bodies may be grown undoped. In that case, the preferable film thickness of the entire first cap layer is 15 to 150 mm when the combination of InGaN / GaN, InGaN / AlGaN, and InGaN / GaN / AlGaN is adopted as the structure of the laminate. When employing the combination of 15 to 100 mm. As a result, a nitride semiconductor laser element having a large impurity compensation suppressing effect can be obtained as in the case where the first cap layer is provided as a single layer. When the first cap layer 108a is formed by stacking two or more kinds of gallium nitride compound semiconductors, the band gap of each layer included in the first cap layer 108a is directed from the active layer side to the p-cladding layer side. It is preferable to increase the size sequentially.
[0028]
The Si diffused from the n-type active layer 107 to the first cap layer 108a gradually increases from the interface with the n-type active layer 107 toward the interface with the second cap layer 108b in the first cap layer 108a. The concentration is lowered. Conversely, Mg diffused from the second cap layer 108b to the first cap layer 108a is directed from the interface with the second cap layer 108b to the interface with the n-type active layer 107 in the first cap layer. The concentration gradually decreases. Mg and Si contained in the first cap layer 108a due to thermal diffusion from the n-type active layer 107 and the second cap layer 108b are 1.0 × 10 6 each.¹⁷cm^-3It is as follows. Note that when the first cap layer 108a is grown, impurities such as Si and Mg are formed at a low concentration (the final concentration after thermal diffusion from the active layer and the second cap layer is 1 × 10¹⁷cm^-3It is also possible to grow while doping (with a low concentration such that: Since the first cap layer 108a contains substantially the same amount of both n-type and p-type impurities, the result is i-type.
[0029]
The first cap layer 108 a is preferably grown at substantially the same temperature (about 900 ° C.) as the active layer 107 in order to suppress In dissociation in the active layer 107. When grown at a lower temperature than the active layer 107, In may be diffused from the active layer 107. When grown at a higher temperature than the active layer 107, In in the active layer is easily dissociated.
[0030]
On the other hand, the second cap layer 108b plays a role of supplying holes to the active layer 107 and confining electrons to the active layer._zGa_{1- z}In the N layer (0 <z <1, more preferably 0.1 <z <0.5), Mg is 8.0 × 10 as a p-type impurity.¹⁸~ 2.0 × 10¹⁹cm^-3It is doped to a concentration of The second cap layer 108b is preferably grown at a high temperature of 1000 ° C. or higher in order to obtain a thin film with good crystallinity. Mg doped in the second cap layer 108b is thermally diffused toward the base layer, but is hardly mixed with Si diffused from the n-type active layer 107 because of the first cap layer 108a. Therefore, almost all Mg doped in the second cap layer 108 contributes to effective carrier generation, and more than the conventional p-type cap layer formed directly on the n-type active layer. Equivalent laser oscillation can be obtained with a small amount of Mg doping.
[0031]
The n-type impurity concentration of the layer made of a gallium nitride compound semiconductor to which an n-type impurity closest to the first cap layer is added among the active layers is 5.0 × 10.¹⁷~ 1.0 × 10¹⁹cm^-3It is preferable that
[0032]
Hereinafter, the details of the structure of the nitride semiconductor laser shown in FIG. 1 will be described. As the substrate 101, GaN is preferably used, but a different kind of substrate different from the nitride semiconductor may be used. Examples of the heterogeneous substrate include sapphire and spinel (MgA1) whose main surface is any one of the C-plane, R-plane, and A-plane.₂O_FourIt is possible to grow a nitride semiconductor such as an insulating substrate such as SiC (including 6H, 4H, 3C), ZnS, ZnO, GaAs, Si, and an oxide substrate lattice-matched with a nitride semiconductor. A substrate material different from that of a nitride semiconductor can be used. Preferable heterogeneous substrates include sapphire and spinel. Further, the heterogeneous substrate may be off-angle, and in this case, it is preferable to use a step-off-angle substrate because the underlying layer made of gallium nitride grows with good crystallinity. Further, when a heterogeneous substrate is used, a nitride semiconductor as a base layer before forming the element structure is grown on the heterogeneous substrate, and then the heterogeneous substrate is removed by a method such as polishing to obtain a single substrate of the nitride semiconductor An element structure may be formed, or a method of removing the heterogeneous substrate after the element structure is formed may be used.
[0033]
In the case of using a heterogeneous substrate, if the element structure is formed through a base layer made of a buffer layer (low temperature growth layer) and a nitride semiconductor (preferably GaN), the growth of the nitride semiconductor becomes good. In addition, when a nitride semiconductor grown by ELOG (Epitaxially Laterally Overgrowth) is used as a base layer (growth substrate) provided on a different substrate, a growth substrate having good crystallinity can be obtained. As a specific example of the ELOG growth layer, a nitride semiconductor layer is grown on a heterogeneous substrate, a mask region formed by providing a protective film on which the nitride semiconductor growth is difficult, and a nitride semiconductor are formed. A non-mask region to be grown is provided in a stripe shape, and a nitride semiconductor is grown from the non-mask region, so that the growth in the lateral direction is achieved in addition to the growth in the film thickness direction. There is also a layer formed by growing a nitride semiconductor. In another form, the nitride semiconductor layer grown on the different kind of substrate may be provided with an opening, and the film may be formed by lateral growth from the side of the opening.
[0034]
On the substrate 101, an n-type contact layer 103, which is an n-type nitride semiconductor layer, a crack prevention layer 104, an n-type cladding layer 105, and an n-type light guide layer 106 are formed via a buffer layer 102. . Other layers other than the n-type cladding layer 105 may be omitted depending on the element. The n-type nitride semiconductor layer needs to have a wider band gap than that of the active layer at least in a portion in contact with the active layer, and therefore, preferably has a composition containing Al. Each layer may be grown while doping with n-type impurities to be n-type, or may be grown undoped to be n-type.
[0035]
An active layer 107 is formed on the n-type nitride semiconductor layers 103 to 106. As described above, the active layer 107 is formed of In._x1Ga_{1- x1}N well layer (0 <x1 <1) and In_x2Ga_{1- x2}It has an MQW structure in which N barrier layers (0 ≦ x2 <1, x1> x2) are alternately and repeatedly stacked an appropriate number of times. The well layers are formed undoped, and all the barrier layers are preferably n-type impurities such as Si and Sn, preferably 1 × 10.¹⁷~ 1x10¹⁹cm^-3It is formed by doping at a concentration of.
[0036]
On the active layer 107, a first cap layer 108a and a second cap layer 108b are formed. As described above, the first cap layer 108a is formed undoped, but contains an n-type impurity such as Si due to diffusion from the active layer 107 serving as a base, and is grown next. A p-type impurity such as Mg is contained by diffusion from the cap layer 108b. Therefore, the n-type impurity concentration in the first cap layer 108a is lower than that of the active layer 107, and the p-type impurity concentration in the first cap layer 108a is lower than that of the second cap layer 108b. 10¹⁷cm^-3It becomes as follows.
[0037]
The second cap layer 108b is made of a p-type nitride semiconductor having an Al mixed crystal ratio higher than that of the p-type cladding layer 110, preferably Al._zGa_{1- z}N (0.1 <z <0.5). Further, a p-type impurity such as Mg is 8 × 10¹⁸~ 2x10¹⁹cm^{- 3}Is doped at a concentration of
[0038]
A p-type light guide layer 109, a p-type cladding layer 110, and a p-type contact layer 111 are formed on the second cap layer 108b. Other layers other than the p-type cladding layer 110 may be omitted depending on the element. These p-type nitride semiconductor layers are required to have a band gap wider than that of the active layer at least in a portion in contact with the active layer, and therefore, a composition containing Al is preferable. Each layer may be grown while doping with p-type impurities to be p-type, or p-type impurities may be diffused from other adjacent layers to be p-type.
[0039]
The first cap layer and the second cap layer are preferably formed (offset) with respect to the active layer such that the band gap energy increases as the distance from the active layer increases. That is, the first cap layer is formed of a layer having a band gap energy larger than that of the active layer (or a well layer when the active layer has a multiple quantum well structure), and the second cap layer is more than the first cap layer. The layer has a large band gap energy. With such a configuration, electrons are confined most efficiently and carrier overflow can be suppressed. As a preferable form, a layer adjacent to the first cap layer in the active layer is In._xGa_{1- x}N layer (0 <x <1), first cap layer is GaN layer, second cap layer is Al_yGa_{1- y}N layer (0 <y <1) or a layer adjacent to the first cap layer in the active layer is In_xGa_{1- x}N layer (0 <x <1), first cap layer is GaN layer and Al_yGa_{1- y}N layer (0 <y <1) is formed in order, the second cap layer is Al_zGa_{1- z}The N layer (y <z, 0 <z <1) may be mentioned, and these two forms are particularly good when the crystallinity is close to that of the active layer, and the lifetime of the laser element can be extended.
[0040]
The n-type nitride semiconductor layer and the p-type nitride semiconductor layer have a structure in which a light guide layer is provided, particularly in a laser device and an edge emitting device, and a structure in which a waveguide is provided by the light guide layer. It becomes. The p-side light guide layer is formed between the second cap layer and the p-side cladding layer, and is preferably formed in contact with the second cap layer. This optical guide layer has a larger band gap energy than the well layer in the active layer, and a good waveguide is provided by reducing the refractive index difference between the active layer and the optical guide layer. A superlattice structure or a single film may be formed. By forming it with a single film, the current flows more easily than in the case of using a superlattice, and V_fCan be lowered. In that case, the film thickness of the single film is at least a film thickness that does not have a quantum effect, preferably a film thickness larger than any of the barrier layer, the first cap layer, and the second cap layer, more preferably It is preferable to form with a film thickness of 300 mm or more.
[0041]
Among the p-type nitride semiconductor layers, a ridge stripe is formed up to the middle of the p-type light guide layer 109. Further, the protective films 161 and 162, the p-type electrode 120, the n-type electrode 121, the p-pad electrode 122, and the n-pad An electrode 123 is formed to constitute a semiconductor laser.
[0042]
【Example】
As an example, a gallium nitride compound semiconductor laser having the structure shown in FIG. 1 will be described below. In each of Examples 1 to 7, the first cap layer is grown undoped, but the concentrations of the n-type impurity and the p-type impurity present in the first cap layer as the final laser element are as follows. 1.0 × 10¹⁷cm^-3It becomes as follows.
[Example 1]
(Substrate 101)
As the substrate, a nitride semiconductor grown on a heterogeneous substrate, in this embodiment, GaN is grown as a thick film (100 μm), and then the heterogeneous substrate is removed and a nitride semiconductor substrate made of 80 μm GaN is used. A detailed method of forming the substrate is as follows. A heterogeneous substrate made of sapphire with a 2-inch φ and C-plane as the main surface is set in a MOVPE reaction vessel, and the temperature is set to 500 ° C., and trimethylgallium (TMG), ammonia (NH_Three), And a buffer layer made of GaN is grown to a thickness of 200 mm, then the temperature is raised, and undoped GaN is grown to a thickness of 1.5 μm to form a base layer. Next, a plurality of striped masks are formed on the surface of the underlying layer, and a nitride semiconductor, GaN in this embodiment is selectively grown from the mask opening (window), and growth accompanied by lateral growth (ELOG) The nitride semiconductor layer formed in step 1) is further grown in a thick film, and the heterogeneous substrate, the buffer layer, and the base layer are removed to obtain a nitride semiconductor substrate. At this time, the mask during selective growth is SiO.₂The mask width is 15 μm and the opening (window) width is 5 μm.
[0043]
(Buffer layer 102)
On the nitride semiconductor substrate, the temperature is set to 1015 ° C., and TMG (trimethylgallium), TMA (trimethylaluminum), and ammonia are used._0.05Ga_0.95A buffer layer 102 made of N is grown to a thickness of 4 μm. This layer functions as a buffer layer between the AlGaN n-type contact layer and the nitride semiconductor substrate made of GaN.
[0044]
(N-type contact layer 103)
Next, TMG, TMA, ammonia, Si-doped Al at 1015 ° C. using TMG, TMA, ammonia, silane gas as impurity gas on the obtained buffer layer 102_0.05Ga_0.95An n-type contact layer 103 made of N is grown to a thickness of 4 μm.
[0045]
(Crack prevention layer 104)
Next, using TMG, TMI (trimethylindium), and ammonia, the temperature is set to 900 ° C. and In_0.06Ga_0.94A crack prevention layer 104 made of N is grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.
[0046]
(N-type cladding layer 105)
Next, the temperature is set to 1015 ° C., TMA, TMG, and ammonia are used as source gases, and undoped Al_0.05Ga_0.95A layer of N is grown to a thickness of 25 mm, then TMA is stopped, silane gas is used as impurity gas, and Si is 5 × 10 5¹⁸/ Cm³A B layer made of doped GaN is grown to a thickness of 25 mm. Then, this operation is repeated 200 times, and the A layer and the B layer are laminated to grow an n-type cladding layer 106 made of a multilayer film (superlattice structure) having a total film thickness of 1 μm. At this time, if the Al mixed crystal ratio of undoped AlGaN is in the range of 0.05 or more and 0.3 or less, a refractive index difference that sufficiently functions as a cladding layer can be provided.
[0047]
(N-type light guide layer 106)
Next, at the same temperature, TMG and ammonia are used as source gases, and an n-type light guide layer 106 made of undoped GaN is grown to a thickness of 0.15 μm. Further, an n-type impurity may be doped.
[0048]
(Active layer 107)
Next, the temperature is set to 900 ° C., TMI (trimethylindium), TMG, and ammonia are used as source gas, silane gas is used as impurity gas, and Si is 5 × 10 5.¹⁸/ Cm³Doped In_0.05Ga_0.95The barrier layer (B) made of N has a thickness of 140 mm, the silane gas is stopped, and undoped In_0.1Ga_0.9The well layer (W) made of N has a thickness of 40 mm, and the barrier layer (B) and the well layer (W) are (B) / (W) / (B) / (W). Laminate in the order of B). The final layer is a barrier layer. The active layer 107 has a multiple quantum well structure (MQW) with a total film thickness of about 500 mm.
[0049]
(First cap layer 108a)
Next, TMA, TMG, and ammonia are used as source gases at the same temperature, and a first cap layer 108a made of GaN is grown to a thickness of 75 mm.
[0050]
(Second cap layer 108b)
Next, the temperature is raised to 1000 ° C., TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienyl magnesium) is used and Mg is 7.5 × 10¹⁸/ Cm³Doped Al_0.3Ga_0.7A second cap layer 108b made of N is grown to a thickness of 100cm.
[0051]
(P-type light guide layer 109)
Next, the temperature is set to 1000 ° C., TMG and ammonia are used as source gases, and a p-type light guide layer 109 made of undoped GaN is grown to a thickness of 0.15 μm. The p-type light guide layer 109 is grown as undoped, but the Mg concentration is 5 × 10 5 due to diffusion of Mg from adjacent layers such as the p-type electron confinement layer 108 and the p-type cladding layer 109.¹⁶/ Cm^ThreeAnd p-type. This layer may be intentionally doped with Mg during growth.
[0052]
(P-type cladding layer 110)
Subsequently, undoped Al at 1000 ° C._0.05Ga_0.95Grow a layer of N with a thickness of 25 mm, then stop TMA, Cp₂Using Mg, a layer made of Mg-doped GaN is grown to a thickness of 25 mm, and this is repeated 90 times to grow a p-type cladding layer 110 made of a superlattice layer having a total thickness of 0.45 μm. When a p-type cladding layer is made of a superlattice in which at least one nitride semiconductor layer containing Al is included and nitride semiconductor layers having different bandgap energies are stacked, impurities are heavily doped in either one of the layers. Although so-called modulation doping tends to improve the crystallinity, both may be doped in the same manner. The cladding layer 110 is a nitride semiconductor layer containing Al, preferably Al_XGa_1-XA superlattice structure including N (0 <X <1) is desirable, and a superlattice structure in which GaN and AlGaN are stacked is more preferable. By making the p-side cladding layer 110 a superlattice structure, the Al mixed crystal ratio of the entire cladding layer can be increased, so that the refractive index of the cladding layer itself is reduced and the band gap energy is increased. It is very effective in lowering. Furthermore, since the superlattice is used, the number of pits generated in the clad layer itself is less than that not formed in the superlattice, so that the occurrence of a short circuit is also reduced.
[0053]
(P-type contact layer 111)
Finally, at 1000 ° C., Mg is deposited on the p-type cladding layer 110 by 1 × 10²⁰/cm^ThreeA p-type contact layer 111 made of doped p-type GaN is grown to a thickness of 150 mm. The p-type contact layer 111 is made of p-type In_XAl_YGa_1-XYN (0.ltoreq.X, 0.ltoreq.Y, X + Y.ltoreq.1), preferably Mg doped GaN, provides the most preferable ohmic contact with the p-electrode 120. Since the contact layer 111 is a layer for forming an electrode, 1 × 10¹⁷/cm^ThreeIt is desirable to have the above high carrier concentration. 1 × 10¹⁷/cm^ThreeIf it is lower than that, it tends to be difficult to obtain a preferable ohmic with the electrode. Furthermore, when the composition of the contact layer is GaN, a preferable ohmic with the electrode material is easily obtained. After the completion of the reaction, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
[0054]
After growing the nitride semiconductor and laminating each layer as described above, the wafer is taken out of the reaction vessel, and SiO 2 is deposited on the surface of the uppermost p-type contact layer.₂A protective film is formed, and SiCl is formed using RIE (reactive ion etching)._FourEtching with a gas exposes the surface of the n-type contact layer 103 where the n-electrode is to be formed, as shown in FIG. In order to etch a nitride semiconductor deeply in this way, a protective film is SiO.₂Is the best.
[0055]
Next, a ridge stripe is formed as the above-described stripe-shaped waveguide region. First, a Si oxide (mainly SiO 2) is formed on almost the entire surface of the uppermost p-type contact layer (upper contact layer) by a PVD apparatus.₂) Is formed to a thickness of 0.5 μm, a mask having a predetermined shape is put on the first protective film 161, and CF is performed by an RIE (reactive ion etching) apparatus._FourA first protective film 161 having a stripe width of 1.6 μm is formed by gas using a photolithography technique. At this time, the height (etching depth) of the ridge stripe is such that the p-type contact layer 111, the p-type cladding layer 109, and a part of the p-type light guide layer 110 are etched to form a film of the p-type light guide layer 109. It is formed by etching to a depth at which the thickness becomes 0.1 μm.
[0056]
Next, after forming the ridge stripe, a Zr oxide (mainly ZrO) is formed on the first protective film 161.₂The second protective film 162 is formed continuously on the first protective film 161 and on the p-type light guide layer 109 exposed by etching with a thickness of 0.5 μm.
[0057]
After the formation of the second protective film 162, the wafer is heat-treated at 600 ° C. In this way SiO₂When a material other than the above is formed as the second protective film, by performing a heat treatment at 300 ° C. or higher, preferably 400 ° C. or higher and below the decomposition temperature of the nitride semiconductor (1200 ° C.) after the second protective film is formed, Since the second protective film is difficult to dissolve in the dissolving material (hydrofluoric acid) of the first protective film, it is more desirable to add this step.
[0058]
Next, the wafer is immersed in hydrofluoric acid, and the first protective film 161 is removed by a lift-off method. As a result, the first protective film 161 provided on the p-type contact layer 111 is removed, and the p-type contact layer is exposed. As described above, as shown in FIG. 1, the second protective film 162 is formed on the side surface of the ridge stripe and the plane continuous therewith (exposed surface of the p-type light guide layer 109).
[0059]
Thus, after the first protective film 161 provided on the p-type contact layer 112 is removed, the exposed surface of the p-type contact layer 111 is made of Ni / Au as shown in FIG. A p-electrode 120 is formed. However, the p-electrode 120 has a stripe width of 100 μm and is formed over the second protective film 162 as shown in FIG. After the formation of the second protective film 162, a striped n-electrode 121 made of Ti / Al is formed in a direction parallel to the stripe on the surface of the n-type contact layer 103 that has already been exposed.
[0060]
Next, in order to form an n-electrode, the p and n-electrodes are etched and exposed on the exposed surface, and a desired region is masked to provide a take-out electrode.₂And TiO₂After providing the dielectric multilayer film 164 formed, the take-out (pad) electrodes 122 and 123 made of Ni—Ti—Au (1000 to 1000 to 8000) were provided on the p and n electrodes, respectively. At this time, the width of the active layer 107 is 200 μm (width in the direction perpendicular to the resonator direction), and SiO 2 is also formed on the resonator surface (reflection surface side).₂And TiO₂A dielectric multilayer film is provided.
[0061]
After forming the n-electrode and the p-electrode as described above, a bar is formed on the nitride semiconductor M-plane (GaN M-plane, (1 1-0 0), etc.) in a direction perpendicular to the stripe-shaped electrode. Then, a bar-shaped wafer is further divided to obtain a laser element. At this time, the resonator length is 650 μm.
[0062]
Threshold value 2.8 kA / cm at room temperature²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The lifetime of the laser element is about 2000 hours at 60 ° C. and 5 mW continuous oscillation, and the characteristic temperature is improved compared to the comparative example described later.
[0063]
[Example 2]
A nitride gallium compound semiconductor laser is fabricated in the same manner as in Example 1 except for the first cap layer 108a. The first cap layer 108a is grown at a temperature of 900 ° C. using TMA, TMG and ammonia as source gases as undoped Al0.3Ga0.7N with a film thickness of about 35 mm. This gallium nitride-based compound semiconductor laser also exhibits the same life and characteristic temperature as in Example 1.
[0064]
[Example 3]
A nitride gallium compound semiconductor laser is fabricated in the same manner as in Example 1 except for the first cap layer 108a. The temperature of the first cap layer 108a is set to 900 ° C., TMI (trimethylindium), TMG, and ammonia are used as source gases, and undoped In_0.05Ga_0.95N is grown with a film thickness of about 100 mm. This gallium nitride-based compound semiconductor laser also exhibits the same life and characteristic temperature as in Example 1.
[0065]
[Example 4]
A nitride gallium compound semiconductor laser is fabricated in the same manner as in Example 3 except that the final layer of the active layer 107 is a well layer having a thickness of about 40 mm and the thickness of the first cap layer 108a is about 60 mm. This gallium nitride-based compound semiconductor laser also exhibits the same life and characteristic temperature as in Example 1.
[0066]
[Example 5]
A gallium nitride-based compound semiconductor laser is fabricated in the same manner as in Example 1 except that the active layer 107, the first cap layer 108a, and the second cap layer 108b are grown as follows.
(Active layer 107)
Next, the temperature is set to 900 ° C., TMI (trimethylindium), TMG, and ammonia are used as source gas, silane gas is used as impurity gas, and Si is 5 × 10 5.¹⁸/ Cm³Doped In_0.05Ga_0.95The barrier layer (B) made of N has a thickness of 140 mm, the silane gas is stopped, and undoped In_0.1Ga_0.9The well layer (W) made of N has a thickness of 70 mm, and the barrier layer (B) and the well layer (W) are (B) / (W) / (B) / (W). Laminate in the order of B). The final layer is a barrier layer, and only the final layer has a Si doping amount of 1 × 10¹⁸/ Cm³And The active layer 107 has a multiple quantum well structure (MQW) with a total film thickness of 560 mm.
[0067]
(First cap layer 108a)
Next, at the same temperature, TMA, TMG and ammonia are used as source gases, and Al_0.15Ga_0.85A first cap layer 108a made of N is grown to a thickness of 30 mm.
[0068]
(Second cap layer 108b)
Next, the temperature is raised to 1000 ° C., TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienyl magnesium) is used and Mg is 7.5 × 10¹⁸/ Cm³Doped Al_0.25Ga_0.75A second cap layer 108b made of N is grown to a thickness of 70 mm.
The laser element thus obtained has a threshold value of 2.8 kA / cm at room temperature.²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The element lifetime of the laser element is about 3500 hours at 60 ° C. and 5 mW continuous oscillation, and the characteristic temperature is improved compared to the comparative example described later.
[0069]
[Example 6]
A gallium nitride-based compound semiconductor laser is fabricated in the same manner as in Example 5 except that the first cap layer 108a and the second cap layer 108b are grown as follows.
[0070]
(First cap layer 108a)
At 900 ° C., TMA, TMG, and ammonia are used as source gases, and a first cap layer 108a made of GaN is grown to a thickness of 30 mm.
[0071]
(Second cap layer 108b)
Next, the temperature is raised to 1000 ° C., TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienyl magnesium) is used and Mg is 7.5 × 10¹⁸/ Cm³Doped Al_0.25Ga_0.75A second cap layer 108b made of N is grown to a thickness of 100cm.
The laser element thus obtained has a threshold value of 2.8 kA / cm at room temperature.²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The lifetime of the laser element is about 3000 hours at 60 ° C. and 5 mW continuous oscillation, and the characteristic temperature is improved compared to the comparative example described later.
[0072]
[Example 7]
A gallium nitride-based compound semiconductor laser is fabricated in the same manner as in Example 1 except that the active layer 107, the first cap layer 108a, and the second cap layer 108b are grown as follows.
(Active layer 107)
Next, the temperature is set to 900 ° C., TMI (trimethylindium), TMG, and ammonia are used as source gas, silane gas is used as impurity gas, and Si is 5 × 10 5.¹⁸/ Cm³Doped In_0.05Ga_0.95The barrier layer (B) made of N has a thickness of 140 mm, the silane gas is stopped, and undoped In_0.1Ga_0.9The well layer (W) made of N has a thickness of 70 mm. The barrier layer (B) and the well layer (W) are (B) / (W) / (B) / (W). Laminate in the order of B). The final layer is a barrier layer, and the Si doping amount is 1 × 10¹⁸/ Cm³In_0.05Ga_0.95N layer (thickness is 100 mm), undoped In_0.05Ga_0.95It is assumed that two layers of N (thickness: 50 mm) are sequentially stacked. The active layer 107 has a multiple quantum well structure (MQW) with a total film thickness of 570 mm.
[0073]
(First cap layer 108a)
Next, at the same temperature, TMA, TMG and ammonia are used as source gases, and Al_0.15Ga_0.85A first cap layer 108a made of N is grown to a thickness of 30 mm.
[0074]
(Second cap layer 108b)
Next, the temperature is raised to 1000 ° C., TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienyl magnesium) is used and Mg is 7.5 × 10¹⁸/ Cm³Doped Al_0.25Ga_0.75A second cap layer 108b made of N is grown to a thickness of 70 mm.
The laser element thus obtained has a threshold value of 2.8 kA / cm at room temperature.²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The lifetime of the laser element is about 2800 hours at 60 ° C. and 5 mW continuous oscillation, and the characteristic temperature is improved compared to the comparative example described later.
[0075]
[Modification 1]
Next, as a modification, the active layer 107, the first cap layer 108a, and the second cap layer 108b are grown as follows. Otherwise, the gallium nitride compound semiconductor laser is fabricated in the same manner as in Example 1.
(Active layer 107)
Next, the temperature is set to 900 ° C., TMI (trimethylindium), TMG, and ammonia are used as source gas, silane gas is used as impurity gas, and Si is 5 × 10 5.¹⁸/ Cm³Doped In_0.05Ga_0.95The barrier layer (B) made of N has a thickness of 140 mm, the silane gas is stopped, and undoped In_0.1Ga_0.9The well layer (W) made of N has a thickness of 70 mm, and the barrier layer (B) and the well layer (W) are (B) / (W) / (B) / (W). Laminate in the order of B). The final layer is a barrier layer, and only the final layer is undoped. The active layer 107 has a multiple quantum well structure (MQW) with a total film thickness of 560 mm.
[0076]
(First cap layer 108a)
Next, TMA, TMG and ammonia are used as source gases at the same temperature, and a first cap layer 108a made of GaN is grown to a thickness of 30 mm.
[0077]
(Second cap layer 108b)
Next, the temperature is raised to 1000 ° C., TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienyl magnesium) is used and Mg is 7.5 × 10¹⁸/ Cm³Doped Al_0.25Ga_0.75A second cap layer 108b made of N is grown to a thickness of 70 mm.
In this laser element, the layer made of a gallium nitride compound semiconductor to which the n-type impurity closest to the first cap layer 108a is added is an Si-doped barrier layer with an undoped barrier layer and an undoped well layer interposed therebetween. Thus, the total film thickness of the undoped layer between the layer added with the n-type impurity and the layer added with the p-type impurity is 240 mm.
The laser device thus obtained has a shorter life than all the examples, but has a longer life than the first to third comparative examples.
[0078]
[Comparative Example 1]
A gallium nitride-based compound semiconductor laser is fabricated in the same manner as in Example 1 except that the second cap layer 108b is formed directly on the active layer 107 without forming the first cap layer 108a. Threshold value 4.0 kA / cm at room temperature²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The element lifetime of the laser element is about 1000 hours at 60 ° C. and 5 mW continuous oscillation, and the characteristic temperature is about 200K.
[0079]
[Comparative Example 2]
A gallium nitride compound semiconductor laser is fabricated in the same manner as in Example 1 except that the second cap layer 108b is formed directly on the active layer 107 as follows without forming the first cap layer 108a. Make it.
(Second cap layer 108b)
[0080]
Next, the temperature is raised to 1000 ° C., TMA, TMG, and ammonia are used as the source gas, Cp 2 Mg (cyclopentadienyl magnesium) is used as the impurity gas, and Mg is 1.0 × 10 6.¹⁹/ Cm³Doped Al_0.3Ga_0.7A second cap layer 108b made of N is grown to a thickness of 100cm.
Threshold value 2.8 kA / cm at room temperature²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The lifetime of the laser element is about 1000 hours at 60 ° C. and 5 mW continuous oscillation, and the characteristic temperature is about 200K.
[0081]
[Comparative Example 3]
A gallium nitride compound semiconductor laser is fabricated in the same manner as in Example 1 except that the first cap layer 108a and the second cap layer 108b are grown as follows.
[0082]
(First cap layer 108a)
At 900 ° C., TMA, TMG and ammonia are used as source gases, and Cp as impurity gas₂Mg (cyclopentadienyl magnesium) is used and Mg is 1.0 × 10¹⁹/ Cm³A first cap layer 108a made of doped GaN is grown to a thickness of 30 mm.
[0083]
(Second cap layer 108b)
Next, the temperature is raised to 1000 ° C., TMA, TMG and ammonia are used as source gases, and Cp is used as an impurity gas.₂Mg (cyclopentadienyl magnesium) is used and Mg is 7.5 × 10¹⁸/ Cm³Doped Al_0.25Ga_0.75A second cap layer 108b made of N is grown to a thickness of 100cm.
[0084]
The laser element obtained thereby has a shorter life because the p-type impurity in the first cap layer is larger than that in the second cap layer, and the lifetime becomes about 800 hours at 60 ° C. and 5 mW continuous oscillation. Since the p-type impurity of the layer is less than that of the first cap layer, V is lower than that of Example 1._fBecomes higher.
[0085]
【The invention's effect】
According to the present invention, the p-type cap layer formed on the active layer containing In includes the first cap layer having a low impurity concentration (preferably non-doped) and the second cap layer doped with the p-type impurity. 2 can suppress the compensation of donors and acceptors that occur near the interface between the active layer and the p-type cap layer, thereby reducing the p-type impurity concentration of the p-type cap layer and increasing the lifetime and temperature. A gallium nitride-based compound semiconductor element having excellent characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating an embodiment of the present invention.
FIGS. 2 (a) and 2 (b) show an active layer and a p-type cap layer of a gallium nitride-based compound semiconductor device according to the prior art (FIG. 2 (a)) and the present invention (FIG. 2 (b)). It is a schematic diagram which shows the mode of the interface vicinity.
FIG. 3 is a schematic cross-sectional view showing an example of a conventional gallium nitride compound semiconductor device.
[Brief description of symbols]
101 substrate (GaN substrate),
102 buffer layer,
103 n-type contact layer,
104 crack prevention layer,
105 n-type cladding layer,
106 n-type light guide layer,
107 active layer,
108a the first cap layer,
108b the second cap layer;
109 p-type light guide layer,
110 p-type cladding layer,
111 p-type contact layer.

Claims (17)

A gallium nitride system having an active layer made of an n-type gallium nitride compound semiconductor doped with n-type impurities and containing p, and a p-type cladding layer made of a p-type gallium nitride compound semiconductor doped with p-type impurities and containing Al In the compound semiconductor device, between the active layer and the p-type cladding layer,
A first cap layer made of a gallium nitride compound semiconductor;
Laminating a second cap layer made of a p-type gallium nitride compound semiconductor containing Al and doped with a p-type impurity;
The first cap layer includes an n-type impurity having a lower concentration than the active layer and a p-type impurity having a lower concentration than the second cap layer,
The n-type impurity concentration of the first cap layer decreases as the distance from the active layer increases so as to be higher on the side closer to the active layer and lower on the side closer to the second cap layer. The p-type impurity concentration of the layer is high on the side close to the second cap layer, and decreases with increasing distance from the second cap layer so as to be low on the side close to the active layer. Compound semiconductor device.   2. The nitridation according to claim 1, wherein the first cap layer is formed in contact with the active layer, and the second cap layer is formed in contact with the first cap layer. Gallium compound semiconductor device. The concentration of n-type impurities and p-type impurities in the first cap layer is 1.0 × 10 ¹⁷ cm ⁻³ or less, and the concentration of p-type impurities in the second cap layer is 8.0 × 10 ¹⁸ to. The gallium nitride compound semiconductor device according to claim 1, wherein the gallium nitride compound semiconductor device is 2.0 × 10 ¹⁹ cm ⁻³ . The first cap layer is selected from the group consisting of a GaN layer, an In _x Ga _{1- x} N layer (0 <x <1), and an Al _y Ga _{1- y} N layer (0 <y <1). The gallium nitride-based compound semiconductor device according to any one of claims 1 to 3, wherein the gallium nitride-based compound semiconductor device comprises one layer or a laminate thereof.   5. The gallium nitride-based compound semiconductor device according to claim 1, wherein the first cap layer is made of a GaN layer and has a thickness of 15 to 100 mm. The first cap layer is made of _{In x} Ga _1- x N layer (0 <x <1), according to any one of claims 1 to 4, wherein the film thickness is 15~150Å Gallium nitride compound semiconductor device. 5. The device according to claim 1, wherein the first cap layer is made of an Al _y Ga _{1- y} N layer (0 <y <1) and has a thickness of 15 to 50 mm. 6. Gallium nitride compound semiconductor device.   8. The gallium nitride-based compound semiconductor device according to claim 1, wherein a film thickness of the second cap layer is 15 to 500 mm. 9.   The active layer is formed by alternately laminating a well layer made of a gallium nitride compound semiconductor containing In and a barrier layer made of a gallium nitride compound semiconductor to which an n-type impurity is added, and the first cap layer The gallium nitride-based compound semiconductor device according to claim 1, comprising an n-type impurity at a lower concentration than the barrier layer. Among the active layers, the n-type impurity concentration of a layer made of a gallium nitride compound semiconductor to which an n-type impurity closest to the first cap layer is added is 5.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ . The gallium nitride compound semiconductor device according to claim 1, wherein the gallium nitride compound semiconductor device is provided. A gallium nitride system having an active layer made of an n-type gallium nitride compound semiconductor doped with n-type impurities and containing p, and a p-type cladding layer made of a p-type gallium nitride compound semiconductor doped with p-type impurities and containing Al A method for producing a compound semiconductor device, comprising:
A gallium nitride-based compound semiconductor comprising an n-type impurity at a lower concentration than the active layer and a p-type impurity at a lower concentration than the p-type cladding layer between the active layer and the p-type cladding layer. A first cap layer and a second cap layer made of a p-type gallium nitride compound semiconductor doped with p-type impurities and including Al,
The film thickness of the first cap layer is determined by the thermal diffusion length of the n-type impurity doped in the active layer in the first cap layer and the p-type impurity doped in the second cap layer. A method for producing a gallium nitride-based compound semiconductor device, wherein the total length is equal to or less than a total length of the thermal diffusion length shown in the first cap layer. The concentration of the n-type impurity and the p-type impurity in the first cap layer is 1.0 × 10 ¹⁷ cm ⁻³ or less, and the concentration of the p-type impurity in the second cap layer is 8.0 × 10 ¹⁸ to 2. The method for manufacturing a gallium nitride compound semiconductor device according to claim 11, wherein the manufacturing method is 0.0 × 10 ¹⁹ cm ⁻³ .   13. The method of manufacturing a gallium nitride-based compound semiconductor device according to claim 11, wherein the first cap layer is a GaN layer and has a thickness of 15 to 100 mm. 13. The gallium nitride compound according to claim 11, wherein the first cap layer is an In _x Ga _{1- x} N layer (0 <x <1), and the film thickness is 15 to 150 mm. A method for manufacturing a semiconductor device. 13. The gallium nitride compound according to claim 11, wherein the first cap layer is an Al _y Ga _{1- y} N layer (0 <y <1), and the film thickness is 15 to 50 mm. A method for manufacturing a semiconductor device.   The method of manufacturing a gallium nitride-based compound semiconductor device according to any one of claims 11 to 15, wherein the thickness of the second cap layer is 15 to 500 mm. The n-type impurity concentration of a layer made of a gallium nitride compound semiconductor to which an n-type impurity closest to the first cap layer is added among the active layers is 5.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ . The method for manufacturing a gallium nitride-based compound semiconductor device according to any one of claims 11 to 16, wherein:

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